On the Bilateral Filter and Ways to Improve It
May 6th, 2002
SCCM (Scientific Computing and Computation Mathematics Program) Seminar

Additive noise removal from a given signal (also known as de-noising) is an important stage in many applications in signal processing. Various approaches have been proposed throughout the years. This talk focuses on Bayesian smoothing and edge-preserving methods. Classical algorithms in this family are typically based on Weighted Least Squares (WLS), Robust Estimation (RE), and Anisotropic Diffusion (AD). These methods share common features such as adaptivity to the data, formation as optimization problems, and the need for iterative-based restoration. In 1998 Tomasi and Manduchi (CS, Stanford) proposed an alternative heuristic non-iterative filter for noise removal called the bilateral filter. It was shown to give similar and possibly better results compared to the abovementioned iterative approaches.

However, the bilateral filter was proposed as an intuitive tool without theoretical connection to the classical approaches. In this talk the various noise-removal techniques discussed here (WLS, RE, AD, and the bilateral filter) are presented and related theoretically to each other. In particular, it is shown that RE (and AD) could be interpreted as WLS with weights replaced after each iteration. Also, it is shown that the bilateral filter emerges from the Bayesian approach as a single iteration of the Jacobi iterative algorithm for a properly posed smoothness penalty. Based on this observation, it is shown how this new filter can be improved and extended to treat more general reconstruction problems.